One can definitively have both a crossbite and an overbite, as these two conditions affect different planes of the bite. The clinical term for any improper bite relationship is malocclusion, and it is common for a person to exhibit multiple types of misalignment simultaneously. When the upper and lower teeth do not align correctly, it often indicates a complex interaction of dental and skeletal issues. Recognizing that these bite problems can coexist is the first step toward seeking a comprehensive and effective treatment plan.
Understanding Overbites and Crossbites
Overbite refers to the vertical relationship between the upper and lower front teeth when the mouth is closed. It measures how much the upper teeth overlap the lower teeth in a downward direction. A slight overlap, where the upper teeth cover about 10-30% of the lower teeth, is considered a normal bite.
An overbite becomes a malocclusion, sometimes called a deep bite, when the vertical overlap is excessive, often covering more than one-third of the lower teeth. This excessive overlap can be caused by the teeth (dental overbite) or by a size discrepancy between the upper and lower jaws (skeletal overbite). Untreated, a deep overbite can cause the lower front teeth to bite into the gum tissue behind the upper front teeth.
A crossbite describes a lateral or horizontal misalignment of the teeth. It occurs when one or more of the upper teeth sit inside the arch of the lower teeth when biting down, rather than resting outside them. This issue can affect a single tooth or multiple teeth and is categorized by its location.
An anterior crossbite involves the front teeth, where the upper front teeth are positioned behind the lower front teeth. A posterior crossbite, which is more common, affects the back teeth, where the upper molars or premolars bite inside the lower ones. This misalignment often signals an underlying issue with the width of the upper jaw, which may be too narrow relative to the lower jaw.
The Mechanics of Coexistence
The simultaneous presence of a crossbite and an overbite often points to a foundational developmental issue in the jaw structure. Jaw size and shape are influenced by genetics, and an inherited discrepancy can affect both the width (crossbite) and the front-to-back relationship (overbite) of the jaws. For instance, a lower jaw that is too small can contribute to a deep overbite, while a narrow upper jaw can simultaneously result in a crossbite.
Prolonged childhood habits, such as thumb sucking, pacifier use, or persistent mouth breathing, can also exert forces that shape the developing dental arches. These habits can push the upper front teeth forward or downward, increasing the vertical overlap, while simultaneously constricting the upper arch, which encourages a crossbite. The dual problem makes the malocclusion more complex because the jaw may shift laterally to find a comfortable biting position, which can worsen the vertical issue.
Having both conditions compounds the potential functional problems and wear patterns. The uneven forces from the lateral misalignment of the crossbite, combined with the excessive vertical pressure of the overbite, can lead to accelerated wear on tooth surfaces. This can increase the risk for temporomandibular joint (TMJ) disorders, causing symptoms like jaw pain, headaches, and muscle strain. Correcting both dimensions is a functional necessity to protect long-term oral health.
Integrated Correction Planning
Treating a combined crossbite and overbite requires a carefully sequenced plan that addresses both the lateral and vertical dimensions of the bite. Orthodontists must analyze the skeletal and dental components of the malocclusion using diagnostic tools like X-rays and 3D models. The overall goal is to establish a harmonious relationship between the upper and lower jaws and the teeth.
In growing patients, the first stage often involves addressing the skeletal issue contributing to the crossbite. This typically means using a palatal expander to widen a narrow upper jaw, creating space for the upper teeth to sit correctly outside the lower teeth. This initial expansion phase is crucial because it corrects the transverse dimension before moving on to individual tooth alignment.
Once the skeletal width is corrected, or if the malocclusion is primarily dental, treatment begins using fixed appliances or clear aligners. Braces or aligners are then used to manage both the overbite and the remaining alignment issues. Vertical elastics or specialized archwire bends may be incorporated to either intrude (push up) the upper front teeth or extrude (pull down) the back teeth to reduce the excessive vertical overlap.
The treatment process involves the coordination of forces to correct the lateral (crossbite) and vertical (overbite) issues concurrently or sequentially. Because these two problems influence each other, the orthodontist must adjust the treatment plan over time to ensure that correcting one issue does not worsen the other. Successful integrated planning results in an aligned bite that is stable, functional, and reduces the risk of future dental and joint complications.